Dependence of i_Ca amplitudes on fibre dimensions and steady-state activation in single fibres from wt, mdx and MinD mice at 2–3 months and 12–18 months of age.

<p>A, i_max from individual fibres plotted against fibre surface area A revealed a linear relationship. In young fibres (2–3 months, left), the slope was comparable for the three genotypes and did not change in old wt and MinD fibres but was almost flat in mdx fibres (12–18 months, right). B, Activation curves reconstructed from the mean activation d_∞ of all individual fibres of each strain, as given in the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0001762#s2" target="_blank">Methods</a>. There is a perfect match in young fibres that is also reflected in the mean half-activation potentials d_0.5 and slope factors k (C). In fibres from 12–18 months old mice, mdx fibres had significantly right-shifted activation curves. However, when looking at those mdx fibres with overlapping i_max values to wt fibres (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0001762#pone-0001762-g003" target="_blank">Fig. 3 B</a>), these ‘wt-like’ mdx fibres had no difference in their activation curves compared to the ‘mdx-like’ mdx fibres with small i_max values (C). n.s.: not significant. *: P<0.05.